This invention relates to a rubber composition and a vulcanized rubber composition. In more particular, the invention provides a rubber composition which comprises as the main component an ethylene-xcex1-olefin copolymer rubber and/or ethylene-xcex1-olefin-non-conjugated diene copolymer rubber, but is free from any zinc-containing compounds that would cause trouble at the time of use of the final products, as well as a vulcanized rubber composition with improved age resistance obtained by vulcanizing the rubber composition.
There have been widely used for radiator hoses, heater hoses and radiator packings ethylene-xcex1-olefin copolymer rubbers and ethylene-xcex1-olefin-non-conjugated diene copolymer rubbers typically represented by ethylene-propylene rubber (EPM) and ethylene-propylene-non-conjugated diene rubber (EPDM). Usually in such uses, the ethylene-xcex1-olefin copolymer rubber and ethylene-xcex1-olefin-non-conjugated diene copolymer rubber are vulcanized with an organic peroxide and used as a vulcanized rubber. In this instance, it has been a common practice in the rubber technology to incorporate, for the purpose of preventing ageing, a zinc-containing compound typically represented by zinc white (zinc oxide) into the rubber composition as one of the essential ingredients of the composition. However, use of a rubber composition containing a zinc-containing compound as a radiator hose, heater hose or radiator packing causes some problems. Thus, zinc eluted into the cooling medium may cause trouble in the mechanical system, and increase electric conductivity to accelerate electrocorrosion of the system. As the result, cracks disadvantageously develop in the radiator hose, heater hose or radiator packing, and to make matters worse, they tend to increase in size.
In view of the situation, the object of this invention is to provide a rubber composition which comprises as the main component an ethylene-xcex1-olefin copolymer rubber and/or ethylene-xcex1-olefin-non-conjugated diene copolymer rubber, but is free from any zinc-containing compounds that would cause the troubles mentioned above at the time of use of the final products, a vulcanized rubber composition with improved age resistance obtained by vulcanizing the rubber composition, and a radiator hose, heater hose and radiator packing obtained by using the vulcanized rubber composition.
The present inventor has made extensive study to achieve the above-mentioned object and resultantly attained this invention.
Thus, the first aspect of this invention relates to a rubber composition which comprises the following components (A)-(D) and is free from any zinc-containing compounds:
(A): an ethylene-xcex1-olefin copolymer rubber and/or ethylene-xcex1-olefin-non-conjugated diene copolymer rubber,
(B): magnesium oxide,
(C): carbon black,
(D): at least one compound selected from the group consisting of the following compounds (D-1)-(D-3):
(D-1): compounds containing a thio group and a carboxylic acid ester group in the molecule,
(D-2): compounds containing a phenolic hydroxyl group in the molecule,
(D-3): compounds containing an acyl group and an imino group in the molecule.
The second aspect of this invention relates to a vulcanized rubber composition obtained by vulcanizing the above-mentioned rubber composition with an organic peroxide.
The third aspect of this invention relates to a radiator hose, heater hose or radiator packing comprising the above-mentioned vulcanized rubber composition.
Component (A) of this invention is an ethylene-xcex1-olefin copolymer rubber and/or ethylene-xcex1-olefin-non-conjugated diene copolymer rubber. The xcex1-olefin in the ethylene-xcex1-olefin copolymer rubber and the ethylene-xcex1-olefin-non-conjugated diene copolymer rubber can be, for example, propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene and 1-decene, and particularly preferred among them is propylene. The non-conjugated diene can be, for example, chain-like non-conjugated dienes, such as 1,4-hexadiene, 1,6-octadiene, 2-methyl-1,5-hexadiene, 6-methyl-1,5-heptadiene and 7-methyl-1,6-octadiene; cyclic non-conjugated dienes, such as cyclohexadiene, dicyclopentadiene, methyltetrahydroindene, 5-vinylnorbornene, 5-ethylidene-2-norbornene, 5-methylene-2-norbornene, 5-isopropylidene-2-norbornene, and 6-chloromethyl-5-isopropenyl-2-norbornene; and trienes, such as 2,3-diisopropylidene-5-norbornene, 2-ethylidene-3-isopropylidene-5-norbornene, 2-propenyl-2,2-norbornadiene, 1,3,7-octatriene and 1,4,9-decatriene. The ethylene-xcex1-olefin-non-conjugated diene copolymer rubber can include one, two or more of these non-conjugated dienes. Particularly preferred among them are 1,4-hexadiene, dicyclopentadiene and 5-ethylidene-2-norbornene. The ethylene-xcex1-olefin copolymer rubber or the ethylene-xcex1-olefin-non-conjugated diene copolymer rubber can be used as oil-extended rubbers containing an extending oil.
The molar ratio of ethylene to xcex1-olefin (ethylene/xcex1-olefin) in component (A) is usually in the range of 40/60-85/15. When a diene is used, the diene content is not more than 20% by weight relative to the total weight of the ethylene, xcex1-olefin and diene.
Component (B) of this invention is magnesium oxide, which is also called magnesia. The magnesium oxide used is not particularly limited and can be those commonly used in the art.
The amount of component (B) used ranges preferably 1-40 parts by weight, more preferably 3-20 parts by weight, relative to 100 parts by weight of component (A). When the amount of component (B) is too small, the age resistance of the vulcanized rubber composition is insufficient in some cases; whereas when it is too large, the age resistance-improving effect hits a ceiling to result in economical disadvantage in some cases. When an oil-extended rubber is used as component (A), the weight of component (A) (100 parts by weight) used as the basis for the other components does not include the weight of the extending oil.
Component (C) of this invention is carbon black and is used for securing high levels of strength and weather resistance of the vulcanized rubber composition. The amount of component (C) used ranges preferably 10-200 parts by weight, more preferably 40 -140 parts by weight, relative to 100 parts by weight of component (A).
Component (D) of this invention is at least one compound selected from the group consisting of the following compounds (D-1)-(D-3):
(D-1): compounds containing a thio group and a carboxylic acid ester group in the molecule,
(D-2): compounds containing a phenolic hydroxyl group in the molecule,
(D-3): compounds containing an acyl group and an imino group in the molecule.
Compound (D-1) can be for example pentaerythritol-tetrakis(xcex2-lauryl thiopropionate), and xe2x80x9cSumilizer-TP-Dxe2x80x9d (a trade name, mfd. by Sumitomo Chemical Co., Ltd.) can be used as a corresponding product. Compound (D-2) can be for example 3,9-bis[2-[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionyloxy]-1,1-dimethylethyl]-2,4,8,10-tetraoxaspiro[5.5]undecane, and xe2x80x9cSumilizer GA80xe2x80x9d (a trade name, mfd. by Sumitomo Chemical Co., Ltd.) can be used as a corresponding product. Compound (D-3) can be for example 3-(N-salicyloyl)amino-1,2,4-triazole, and ADEKASTAB CDA-1 (a trade name, mfd. by Asahi Denka Kogyo K.K.) can be used as a corresponding product.
The amount of component (D) used ranges preferably 0.5-20 parts by weight, more preferably 1-10 parts by weight, relative to 100 parts by weight of component (A). When the amount of component (D) is too small, the age resistance of the vulcanized rubber composition is insufficient in some cases; whereas when the amount of component (D) is too large, the age resistance-improving effect hits the ceiling to result in economical disadvantage in some cases. When two or more compounds are used as component (D) in combination, the amount of component (D) herein referred to is the sum of the amount of the two or more compounds.
Although component (D) used can be at least one compound selected from the compounds (D-1)-(D-3), a quite high level of age resistance can be attained by using all of compounds (D-1), (D-2) and (D-3) in combination. In this case, the weight ratio of compounds (D-1), (D-2) and (D-3) used ranges preferably (5-8)/1/(4-1).
In this invention, it is important to use magnesium oxide and, additionally, not to use any zinc-containing compounds. In this way, the above-mentioned problems that would be caused by zinc can be dissolved, and the ageing phenomenon, in which such properties as tensile strength, elongation and hardness are deteriorated associated with the use in high temperature air atmosphere, can be prevented.
The vulcanized rubber composition of this invention is a vulcanized product obtained by vulcanizing the above-mentioned rubber composition with an organic peroxide.
The organic peroxides used can be those commonly used for crosslinking rubbers and include, for example, di-t-butyl peroxide, t-butylcumyl peroxide, dicumyl peroxide, xcex1,xcex1-bis(t-butylperoxyisopropyl)-benzene, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3,1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, n-butyl-4,4-bis(t-butylperoxy)valerate, 2,2-bis(t-butylperoxy)-butane and 2,2-bis(t-butylperoxy)octane. These organic peroxides can be used each alone or in combination of two or more thereof.
The amount of the organic peroxide used ranges preferably 1-10 parts by weight, more preferably 2-6 parts by weight, relative to 100 parts by weight of component (A). When the amount used is too small, the crosslinking density obtained is sometimes low, resulting in insufficient mechanical strength of the vulcanized rubber composition; whereas when the amount is too large, such troubles as blistering occur in some cases. For enhancing the crosslinking efficiency of organic peroxide in vulcanization, known crosslinking auxiliaries, for example, p,pxe2x80x2-dibenzoylquinone dioxime, quinone dioxime, triallyl cyanurate, sulfur, ethylene dimethacrylate, N,Nxe2x80x2-m-phenylene bismaleimide, triallyl isocyanurate, trimethylolpropane trimethacrylate and metal salts of acrylic acid can be used.
Preparation of a vulcanized rubber composition by using the rubber composition of this invention can be conducted for example as follows. Thus, components (A)-(D), the organic peroxide and additionally, according to necessity, an antioxidant, vulcanization accelerator, processing auxiliary, stearic acid, reinforcing agent, filler, plasticizer, softener, etc. (provided that these are limited to those which contain no zinc) are blended by using a conventional kneader, such as a roll or Banbury mixer, to obtain a vulcanizable rubber composition, which is then vulcanized at a temperature of preferably 120xc2x0 C. or above, more preferably 150-220xc2x0 C., for about 1-60 minutes to obtain the vulcanized rubber composition. The vulcanization can be conducted by press vulcanization, steam vulcanization and other suitable methods of vulcanization.
The vulcanized rubber composition obtained from the rubber composition of this invention can be processed into radiator hoses, heater hoses and radiator packings by conventional methods. The products thus obtained are quite excellent ones which have the characteristic features described above.
This invention is explained below with reference to Examples and Comparative Examples.